1. Field of the Invention
This invention relates to an optical wavelength conversion device for converting an optical fundamental wave entering the device to an optical second harmonic having a wavelength one half the wavelength of the fundamental wave. This invention particularly relates to an optical waveguide type optical wavelength conversion device. This invention also relates to a method of making an optical waveguide type optical wavelength conversion device having an optical waveguide formed of a crystalline organic nonlinear optical material.
2. Description of the Prior Art
Various attempts have heretofore been made to convert the wavelength of a laser beam to a shorter wavelength by utilization of optical second harmonic generation using a nonlinear optical material. As an optical wavelength conversion device for carrying out wavelength conversion in this manner, there have heretofore been known a bulk crystal type device as disclosed in, for example, Japanese Unexamined Patent Publication No. 51(1976)-2651, and an optical waveguide type device as disclosed in, for example, Japanese Unexamined Patent Publication No. 60(1985)-14222. When the bulk crystal type optical wavelength conversion device and the optical waveguide type optical wavelength conversion device are compared with each other, the latter can confine an optical wave in a smaller region, and therefore can increase the power density and achieve a higher wavelength conversion efficiency than with the former.
Accordingly, in recent years, extensive research has been conducted on the optical waveguide type optical wavelength conversion device. The optical waveguide type optical wavelength conversion device is constituted by a pair of substrates disposed facing each other, and an optical waveguide formed of a nonlinear optical material having a refractive index higher than the refractive indexes of the substrates and formed between the substrates. For example, in the optical wavelength conversion device, phase matching is effected between the guided mode of the fundamental wave through the optical waveguide and the radiation mode of a second harmonic to the substrate section (in the case of Cherenkov radiation).
However, the conventional optical waveguide type optical wavelength conversion device has the drawback in that it is not always possible to achieve entry of the fundamental wave into the device and radiation (take-up) of the second harmonic from the device. Specifically, in many cases, a coupler prism has heretofore been closely contacted with the surface of the substrate for introducing the fundamental wave into the optical wavelength conversion device by the coupler prism. However, when the coupler prism is strongly press fitted to the optical wavelength conversion device (directly to the substrate) in order to achieve close contact therebetween, the optical wavelength conversion device is often broken by the pressing force. Also, the second harmonic has heretofore been radiated from an end face of the optical wavelength conversion device. However, in this case, the phase of the optical wave taken up from the optical wavelength conversion device varies, and therefore it is not always possible to converge the optical wave to a desired beam diameter.